RALEIGH, N.C. — In the last years of his life, the longtime football coach for dominating college teams wrestled with impaired speech, forgetfulness, lapses in concentration. And with his conscience.

His body was betraying him, and now, possibly, so was the sport he loved.

A few years earlier, the coach, Don Horton, had learned that he had Parkinson’s disease, but these new, intensifying infirmities were more commonly linked to chronic traumatic encephalopathy, or C.T.E., a degenerative brain disease caused by repeated hits to the head and linked to football and other contact sports.

Was his deteriorating health, Horton wondered, a consequence of his many years as a football lineman? Even worse, he worried, was he responsible for exposing hundreds of players to the kind of head trauma now impairing his life? After all, as a prominent assistant coach at Boston College and North Carolina State for nearly 20 years, he had recruited and encouraged scores of athletes to play major college football.

In the still of night at home, Horton asked himself what he should say if a parent of a former recruit called to say that a son was suffering from C.T.E.-like symptoms.

“And I would tell him that he could say: ‘I know how it feels,’” his wife, Maura Horton, responded. “And Don didn’t necessarily like that answer. But that’s the truth.”

There was only one way to be sure if he had C.T.E. His brain would have to be examined post-mortem, the only way to confirm the disease since there is no reliable test for the living. At first Horton balked, but as his cognitive difficulties intensified, he relented and even insisted that the findings of his brain examination be made public.

Horton died almost one year ago, on May 28. He was 58. Multiple news reports celebrated his accomplishments, and hundreds of former players and colleagues attended his funeral. Quietly, researchers at Boston University’s C.T.E. Center received his brain; the results would not be revealed for nearly 10 months.

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Horton during a North Carolina State game in 2009. “You could see him struggling sometimes, but he never opened up about it because, I think, he didn’t want to feel like he was letting the group down,” a fellow coach said.CreditEthan Hyman/The News & Observer, via Associated Press

A Life in the Game

In 1997, Horton got the career breakthrough he had been hoping for when he was hired at Boston College, where he earned a reputation as one of college football’s best offensive line coaches.

He had played for Wittenberg University, a Division III power in Ohio, but was drawn to coaching and had spent 15 years traversing the country, landing jobs at Ohio State, New Mexico State, Virginia, Ohio University, Wittenberg, Capital University in central Ohio and Southern Illinois. He had married Maura Sweeney in 1993, and she gave up a sales job for the rolling stone existence of a football coach’s wife.

At Boston College, Horton thrived. Behind dominating offensive line play — Horton coached nearly 20 players who made it to the N.F.L. — the team won seven successive postseason bowl games. He worked for Coach Tom O’Brien, whom Horton had known since his youth.

Horton was known as a gifted recruiter — handwritten notes were a specialty — and for the unusually strong bond he developed with his players, especially off the field.

“He coached me for one year, and yet I had a friend and mentor for life,” said Scott Dragos, a Boston College tight end who went on to play for the Chicago Bears. “Players just gravitated to him regardless of position. He treated the walk-on and the star exactly the same and talked to everyone about life, not just football.”

Josh Beekman, a guard who also played in the N.F.L., said that at Thanksgiving and Easter, when many players could not afford trips home, several would go to the Hortons’ home for meals.

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Horton in a family photo during his playing days. He told his wife that he probably had 15 concussions as a player. “We just played through them,” he told her.

Sometimes a player’s visit to the Hortons lasted even longer. When one Boston College player was suspended from the team and expelled from his dormitory, he lived with the Hortons for three months.

“Don called me and said: ‘When I recruited this kid I told his mother that I’d take care of him,’” Maura said.

The player was eventually reinstated to the team and graduated from Boston College.

O’Brien and most of his staff left Boston College for North Carolina State at the end of 2006. Months earlier, Horton, who was 6 feet 4 inches and maintained a demanding fitness regimen, noticed he was having trouble lifting weights with his left arm. He was 48, and thought it was a pinched nerve. Specialists told him that he had Parkinson’s disease.

Horton’s doctors said he could work for at least 10 more years and maybe live to be 80, Maura Horton said.

“They kept saying that this is not a death sentence,” she said.

The Hortons settled in North Carolina, but over time Horton’s problems grew. The course of a progressive disease like Parkinson’s is not predictable, but Horton was experiencing myriad symptoms, coming at a rapid pace, making his wife question if he had something more.

He had sleep disturbances, hallucinations, memory problems, rigidity, paranoia and eventually coordination issues that led to dangerous falls and losses of consciousness.

Most striking, Maura Horton noticed behavioral changes.

“It wasn’t like he was angry and hitting somebody, but he was short, which Don Horton never was,” she said tearfully, seated in the living room of her North Carolina home. “I hate saying that, because I feel like I’m betraying him. But he had changed. He was totally withdrawn and not engaging. It was not the man I’d known all these years.

“So, to me, things were just not adding up.”

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A Horton family scrapbook. Horton instructed his daughters not to head the ball while playing soccer, aware that some studies had linked it to brain injury.CreditTravis Dove for The New York Times

She began researching Horton’s symptoms and discovered a deluge of stories about C.T.E.

In 2009, seven years before Horton died, she called Chris Nowinski, a co-founder and the chief executive of the Concussion Legacy Foundation, and told him that she thought her husband had C.T.E. She also raised her suspicions with Horton’s doctors, but they said that, even if true, it would not change the course of his treatment.

Horton continued his duties at North Carolina State.

“He never missed a day of work and still produced great offensive linemen,” said Jason Swepson, an assistant coach at North Carolina State at the time. “You could see him struggling sometimes, but he never opened up about it because, I think, he didn’t want to feel like he was letting the group down.”

At home, however, Horton’s illness was leading to a variety of changes, physically and philosophically. His daughters, Libby, 14, and Hadley, 9, had begun playing soccer, but Horton pointedly refused to allow them to head the ball in games or in practices, aware that some studies had linked heading to brain injury.

“Don told them, ‘If I ever see you head the ball, I’ll run onto the field and yank you off myself,’” Maura said.

Although Horton kept his misgivings about football’s potential consequences within his household, he talked about it regularly.

“Don would ask, ‘Are we just carrying this cycle on?’” Maura Horton said. “That was a question I couldn’t answer. But it’s definitely the right question to ask.”

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Maura Horton with her daughters, Libby, left, and Hadley, at home in Raleigh, N.C.CreditTravis Dove for The New York Times

At first, he scoffed when his wife suggested that he donate his brain for C.T.E. testing, saying “‘I’m going to donate my brain just to prove you wrong,’” Maura Horton said.

Affliction, and Opportunity

Over time, however, as more neurological functions began to fail, Horton, in quiet moments at home, accepted that he could have C.T.E. and that it might even present an opportunity.

Much is unknown about the disease, including why, for instance, some players get it and some don’t. Nearly 100 former N.F.L. players have been found to have the disease, including Hall of Famers like Ken Stabler and Junior Seau, but research on college players who did not play professionally is not extensive.

By donating his brain, Horton believed he could aid the science and, ultimately, perhaps help people evaluate whether to play, or continue playing, the game.

“He wanted to make a difference if he could,” said Maura Horton, 47. “Don would never tell someone not to play the game, because he loved football and wouldn’t betray it. But he wanted them to see a full picture to make a full decision.”

She added: “Don said, ‘If they would be more reflective and be more upfront about things that were happening to them, they might get out of the game earlier if they needed to. Kids try to hide so much about what’s really happening.’”

By 2013, Horton had left North Carolina State, but he felt the pull of the game. He became an assistant coach at a high school a few miles from his home in Raleigh. Despite his inner conflict, Maura Horton figured, the game and coaching were too ingrained for him to turn away. He did preach lessening contact at practices.

“Don never perceived the benefit of lining up and just knocking into each other, especially for a lineman who gets hit on every play,” Maura said.

After two seasons at the high school, however, his unstable mobility forced him to leave the position. He stopped driving after a minor auto accident.

Horton still worked out for hours at the gym, believing that exercise would combat his infirmities, but neurological irregularities were sabotaging his body, including his blood pressure. Maura would get a call from the gym because Don had passed out.

On Sunday, May 15, 2016, Horton fell again, opening a gash on his head that required stitches. An ambulance took him to a hospital, and then he entered hospice care. As his family left the facility that night, he turned to say: “Bring home a win.”

Said Maura: “I think he thought we were going to a soccer game or something.”

By the next morning, Horton was no longer speaking. He died two weeks later.

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Horton coaching high school players in 2013. Though he was suffering by then, his wife said, the game was too ingrained for him to turn away.CreditRobert Willett/The News & Observer, via Associated Press

Maura signed the paperwork to have his brain tested and told almost no one about it.

In March, representatives from the Boston University C.T.E. Center and the Concussion Legacy Foundation informed Maura Horton that the examination of her husband’s brain had revealed the presence of C.T.E.

Doctors grade the severity of the disease on a scale from 0 to 4, with 4 being the highest. Horton’s C.T.E. was at stage 3 or 4, according to Dr. Ann McKee, chief of neuropathology at the V.A. Boston Healthcare System and a professor of neurology and pathology at the Boston University School of Medicine.

Dr. McKee, who conducted the examination, also noted that Horton had a “pretty severe” case of Parkinson’s disease, adding that C.T.E. can accelerate the progression of Parkinson’s.

“It is likely that he had C.T.E. originally and that it may have contributed to the early onset of Parkinson’s,” Dr. McKee said.

Maura Horton was not surprised by the diagnosis, and neither was she startled by the overarching question posed afterward by her daughters. They asked: What does it mean?

In the interview, Maura Horton explained the many ways she has interpreted the C.T.E. finding for her daughters, but most often she came back to one point.

While N.F.L. players have become the face of C.T.E. in football, she said, it is just as serious a threat to lesser known ex-players like Horton.

“People read the C.T.E. stories on the N.F.L. level because it’s been so highly publicized, but I don’t think people see it as something the average person gets,” Maura Horton said. “But there are more people who are going to be affected who played in the N.C.A.A. than played in the N.F.L. That’s what I told our girls: It’s going to be average guys like your dad.”

Don Horton never discussed how many concussions he had as a player.

“He would say: ‘We didn’t call them concussions. We called them getting your bell rung,’” Maura Horton said. “And I’d ask him how often that happened, and he said: ‘Probably like 15 times. We just played through them.’”

“But as I’ve told our kids, the number doesn’t matter. It was obviously too many, because he’s no longer with us.”

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A commemorative ball from a 2006 bowl game, part of a string of postseason victories for Horton’s Boston College Eagles.CreditTravis Dove for The New York Times

Numerous former players and colleagues said Horton had not raised the issue of C.T.E. with them. At the same time, they were not surprised he was worried for them.

“When I heard about his C.T.E. diagnosis, my first thought was that Coach Horton was probably more concerned about us and feeling guilty about pushing guys into the game,” Scott Dragos said. “I figured he’d be thinking of others first.”

The Hortons are still big fans of college football and watch the sport almost every Saturday in the fall. At the end of games, Maura Horton gathers her daughters to watch postgame interviews with the coaches.

“I still believe the lessons learned in football are really good,” she said, mentioning things like teamwork, work ethic and learning how to win and lose. “And if it’s something their dad would have said, I want them to hear it. The message is still right even if their dad isn’t there to deliver it.”

At the same time, she wants more former football players, and other athletes, to donate their brains for research.

“Clearly, we don’t know enough about C.T.E., and we need more brains to study,” she said. “We need to continue to do the research to make the game as safe as it can be.”

In the hours after Don Horton died, doctors informed Maura that because Don was only 58, an autopsy would be performed.

When Maura Horton received her husband’s death certificate last year, her eyes were drawn immediately to the cause of death: blunt force trauma to the head.

She was upset because Parkinson’s, which she believed had caused the fall that preceded his death, was not listed on the death certificate.

“Then one night I thought: Maybe that’s poetic justice,” Maura Horton said this month at home, where pictures and reminders of Don are in nearly every room.

“Nobody said when the blunt force trauma happened,” she added. “Maybe that’s what this was all about.”

A version of this article appears in print on , on Page SP1 of the New York edition with the headline: A Battle With C.T.E., And His Conscience. Order Reprints | Today’s Paper | Subscribe